<?php

/**
 * 对微信小程序用户加密数据的解密示例代码.
 *
 * @copyright Copyright (c) 1998-2014 Tencent Inc.
 */
namespace addons\csmsignin\library;

class ErrorCode
{

    public static $OK = 0;

    public static $IllegalAesKey = - 41001;

    public static $IllegalIv = - 41002;

    public static $IllegalBuffer = - 41003;

    public static $DecodeBase64Error = - 41004;
}

class WXBizDataCrypt
{

    private $appid;

    private $sessionKey;

    /**
     * 构造函数
     *
     * @param $sessionKey string
     *            用户在小程序登录后获取的会话密钥
     * @param $appid string
     *            小程序的appid
     */
    public function __construct($appid, $sessionKey)
    {
        $this->sessionKey = $sessionKey;
        $this->appid = $appid;
    }

    /**
     * 检验数据的真实性，并且获取解密后的明文.
     *
     * @param $encryptedData string
     *            加密的用户数据
     * @param $iv string
     *            与用户数据一同返回的初始向量
     * @param $data string
     *            解密后的原文
     *            
     * @return int 成功0，失败返回对应的错误码
     */
    public function decryptData($encryptedData, $iv, &$data)
    {
        if (strlen($this->sessionKey) != 24) {
            return ErrorCode::$IllegalAesKey;
        }
        $aesKey = base64_decode($this->sessionKey);

        if (strlen($iv) != 24) {
            return ErrorCode::$IllegalIv;
        }
        $aesIV = base64_decode($iv);

        $aesCipher = base64_decode($encryptedData);

        $result = openssl_decrypt($aesCipher, "AES-128-CBC", $aesKey, 1, $aesIV);

        $dataObj = json_decode($result);
        if ($dataObj == NULL) {
            return ErrorCode::$IllegalBuffer;
        }
        if ($dataObj->watermark->appid != $this->appid) {
            return ErrorCode::$IllegalBuffer;
        }
        $data = $result;
        return ErrorCode::$OK;
    }
}

